feat: provider-result caching with time expiry + DSL fact-level TTL

Automatically-retrieved facts (balances, sessions, etc.) are now cached with
a time expiry so repeated checks don't re-invoke the underlying data store.

- check(): registered providers cache their normalized edges per
  (relation, subject, object) with a TTL; a fresh entry is reused without
  re-invoking the provider. Per-check factProviders are one-off observations
  and stay cache-transparent (no read, no write).
- TTL resolution: DSL-declared 'BEHAVES { ttl <duration> }' on a fact >
  setFactTTL(relation, ms) > policy.providerCacheTTL (default 30s; 0 disables).
- Grammar: facts may now declare a freshness window via
  'fact balance(user, amount) BEHAVES { ttl 1h }' (previously BEHAVES only
  accepted 'AS edge|transitive|hierarchical|symmetrical_graph'). The runtime
  indexes it as the fact's ttlMs.
- registerFact/unregisterFact, graph mutations (add/update/remove node or
  relation), and invalidateProviderCache(relation?) keep the cache consistent.
- Injectable clock (default wall clock) drives cache freshness, mirroring the
  core's unpinned-clock contract.

Tests: DSLRuntimeCache (reuse within TTL, expiry re-invoke, per-check
override transparency, registerFact invalidation, mutation invalidation,
per-relation/all invalidation, policy default, DSL-declared 1h TTL).

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@arbiter/evidence-dsl",
-  "version": "1.6.0",
+  "version": "1.7.0",
   "description": "Evidence DSL v2 compiler: translates the natural Evidence DSL (ADR-000) into @arbiter/core relation configurations.",
   "license": "ISC",
   "type": "module",